Incandescent filament and lamp



- Nov. 21,1939. G. M|L| 2.1 53

' INCANDESCENT FILAMENT AND LAMP Filed Feb. 13, 1937 2 Sheets-Sheet l INVENTOR 617' 0/1 /7/1 ATTORNEY Nm .21,1939. I G. MIL] 2,180,538

INCANDESCENT FILAMENT lAND LAMP Filed Feb. 13, 1937 2 sheets-sheaf 2 g E l I 1' g i I I 1 l I I I l I l I I 1 I INVENTOR f g 5 ova/v flf/Z/ l0 5 6' so I v BY W ATTORNEY Pam Nov. 31, 1939 4 5 UNITED "STATES PATENT oF cs 2,180,538 a nvcs vnnscnm- AND mm Gjon Mill, Montclair, N. J., assignor to Westinghouse Electric & Manufacturing d y, East Pittsburgh, Pa., a corporation of Pennsyl- Application February 13, 1937, Serial No. 125,548

7 Claims. This invention relates' to lamps having incandescible filaments and more particularly to such a lamp in: which the filament is of a special shape,

in order to provide for a greater uniformity in Q the intensity ,of the light radiated from one side of said filament. A still further object of my invention is .the

production of a special form of filament, which go provides a beam of light more uniform in--in' tensity than beams which have previously been produced.

An additional object of my'invention is the provision of a lamp, especially adapted for use in sound recording and printing, having an incandescible filament in-an inert gas, and operable at such a high temperature, that a substantial proportionof light emitted is in the ultraviolet part of-the spectrum, the bulb of said lamp being formed of glass pervioiis'to such light.

Other objects and advantages of the invention relating to the particular arrangement and construction of the various parts will become apparent as the description proceeds.

In the drawings Fig. l is a diagrammatic view showing one form of an optical recording system with which my lamp may be used.

Fig. 2 is an. enlarged fragmentary view of the motion picture film having a sound track, as shown in Fig. 1.

Fig. 3 is an elevational view, partly in vertical section, of one form of lamp embodying my invention.

Fig.4 is an enlarged horizontal sectional view, onthe line IV-IV of Fig. 3, looking in the direction of the arrows.

Fig. 5 is an elevational view, on a greatly enlarged. scale, of a filament embodying my-invention.

Fig. 6 is a diagram for use in explaining how. more uniform light radiations, are emitted from a filament embodying my invention'than from an ordinary straight coil filament.

'55 Fi 7 is a similar diagram showing an ordinary straight coil filament, for comparison with Fig. 6.

Fig. 8 is a' chart comparing the variation in intensity of the'light from a filament embodying my invention, with that from a similar filament formed as an ordinary straight coil or bar fila- 5 ment. l

Referring to the drawings in detail, like parts being designated by like reference characters, and first considering Figs. 3 and 4-, there is shown a lamp l0 comprising an envelope ll, preferably 10 formed of ultra-violet light transmitting glass, and provided with a base l2.

In the envelope II is sealed. a coil filament l3,

slightly bent'into the shape of an arc of less than 90 provided with substantiallystraight ends ll desirably surrounded by slip-over coils i5, and

;-both ends J4 and coils l5 welded to the upper end portions of leading-in conductors l6, extend- .ing from the press I! of a mount Hi. The lampis desirably of the gas-filled type, thereby adapting the filament to be operated at an abnormally high temperature for the production. of ultraviolet light.

Although I do not wish to be limited to the exact construction of the lamp, I am giving a specific example of a desirable form for the main purpose of my invention.-

The lamp desirably/has an overall length of about 73 m. m., the tungsten filament being positioned about 40.5 mom. from the base pin 19.

'is a length of about 59.1 m. m. exposed. There 6 are desirably 12 turns forming the coil and after the same is wound it isformed so that its inner side, or that nearest the center, curves about a. radius of about H".

The slip-over coils l5 receiving the straight ends are desirably formed of the same size wire as the filament l3, wound on a 13-mll mandrel at 93 turns-per inch, and cut to 3 m. m. lengths.

These slip-over cols on the ends of the filament provide a greater radiating area for said ends, 5 and reduce the temperature at the welds with the leading-in conductors lfiywhioh are desirably formed 'of metal of lower melting point, than tungsten, such as nickel or nickel-iron alloy. A lamp as specifically described above is de- 5 -ly in- Fig. l which discloses one use to which the lamp may be put.

Referring now specifically to Figs. 1 and 2,

there is shown an arrangement for utilizing a lamp embodying my invention for the production of the sound track 20 on a motion-picture film 21. The light from the filament I3 of the lamp I0 is directed by condenser lens 22, positioned nearby, on the mirror 23, desirably forming a part of a magnetic galvanometer (not shown) and vibrated in accordance with the current received by said galvanometer, which current varies in accordance with the sound waves to be recorded.

Close to the condenser lens 22 is a mask formed with an aperture 25 of desired shape, and near the galvanometer mirror 23 is a lens 26 adapted to focus an image 21 of the opening 25 at the plane of a screen 28 having a slit 28 therein. Used in accordance with my invention, it is possible to adjust the spot of light 21 so that it has uniform intensity. Rotation of the gal-,

vanometer mirror causes the spot 21 to move and illuminate more or less of the slit 29, on account of the convergence of its sides 30 and 3I.

If a film were placed directly behind the slit 29 and sound currents passed through the galva nometer, the mirror 23 would vibrate and a sound track, on an enlarged scale would be recorded. The objective lens 32 reduces the size of the image of the illuminated portion of the slit 29 to form the desired sound track 20. The lens 33 serves to direct all the light which passes through the slit 29 upon the objective lens 32. In the example, the film 2| is shown passing over a rotating drum or cylinder 34, under a guiding roller 35.

It is desirable to use a filter 36, as shown in Fig. 1, for the light from the lamp I0, so as to record by ultra-violet light. For this purpose, the visible rays from the lamp I0 may be almost completelyexcluded by the use of such as a No.

584 Corning filter. One advantage of using ultra-violet rather than visible light for recording, is that the sensitive emulsion on the film absorbs ultra-violet. light very strongly. Therefore such light although it is scattered by the silver halide grains, as in the case of visible light recording, does not spread as far. This confines the image to the surface of the film. A high density or high degree of film blackening is obtainable only by relatively long exposures, but all the grains immediately in the vicinity of the exposed surface are developable, whereas with enough visible light exposure to produce the same density, only some grains would be used and the remainder of the density would be contributed by developed grains farther within the emulsion and to either side.

As an alternative, the separate filter 36 may be positioned at a difierent point or dispensed with and the bulb I I formed of glass which filters out substantially all the visible light, like a No. 584 Coming filter..

Fig. 5 is an enlarged representation of a filament I3 embodying my invention and looking at the convex side. On account of the coil having been bent toare shape, to show, at all points in the line of vision from the convex side, substantially the same percentages of inner coil area and directly radiating or outer area, not only is more of the inner surface 31 of each turn exposed to View, but the coil presents an area of greater and more uniform brilliancy than if the coil were straight as ordinarily employed. This will be clear from a comparison of Fig. 6 with Fig. 7.

In Fig. 6 the coil I3 is curved about a desired radius whilein Fig. 7 a similar coil I3 is straight. If the coil I3 is viewed along the line of vision a, it appears as in Fig. 5. If it is viewed along the line ofvision b, atan angle of about ten degrees, for example, to that of a, the point of normal intensity merely shifts with the radius from line a to line b without any substantial variation in the intensity of the light viewed. In a similar way, if the incandescent filament is viewed along the line 0, at an angle of about ten degrees, for example, to that of a, on the other side from that of b, the appearance of the coil is merely that the point of normal brilliancy has shifted from line a. to line-c without any substantial variation in the intensity from the light source.

This is represented graphically in Fig. 8, which shows that the variation in the light from the curved filament, when viewed through the angle beginning ten degrees to one side of the normal and ending ten degrees to the other side of the normal isonly 3 while with a straight coil,

as shown in Fig. 7, the variation is 16%. The

point of maximum curvature.

Referring to Fig. 'l, we see that when viewing the filament I3 along the line a, we get a definite amount of light. When the line of vision is changed to b, we get a smaller amount of light due to the front portions of the turns of the coil I3 shading, to a greater extent, the more highly illuminated inner surfaces of the turns, which receive internal radiations and thereby reflect light as well as radiate it, consequently having greater light-giving capacity. It will be seen that in order to view the filament I3 to get the same light effect from the, point from which the line b starts, it would be necessary to look at it along said line b which is parallel to a. and thus entirely miss the filament. Similar comments apply to the line 0'. It will therefore be seen that the relatively great variation in intensity along the length of the filament 13, as represented by the curve marked straight coil" in Fig. 8, is avoided by using the curved coil, thereby resulting in a negligible variation in intensity, as represented by the' curve marked curved coil in the same figure.

Although a preferred embodiment of my invention has been disclosed, it will be understood that modifications may be made as within the spirit and scope of the appended claims.

I claim:

1. A lamp having an incandescible tungsten coil filament slightly bent into an arc of less than and having substantially straight end portions, supplemental coils formed of a metal of lower melting point than tungsten enclosing over said end portions, leading-in conductors, and said coil covered end portions welded to said leadingin conductors in order to provide a greater radiating substantially straight end portions, so as to present, on its convex side, an area intermediate its ends of greater and more uniform brilliancy, and supplemental coils formed of metal of lower melting point than that of said filament contacting said end portions, and both end portions and supplemental coils welded to said leading-in conductors in order to provide a greater radiating area for said end portions and reduce the operating temperature at said welds.

3. In an incandescent electric lamp, a tungsten filament, a leading-in conductor, a contacting supplemental coil of a metal of lower melting point than tungsten surrounding the end portion of said filament adjacent said conductor, and a weld between said conductor, coil, and coil-surrounded end portion of the filament for increasing the radiating area at said connection.

4. A lamp having an incandescible coil filament with substantially straight end portions, a supplemental coil contacting and surrounding each end portion, leading-in conductors, and a single weld at the junction between each leading-in conductor and the adjacent coil-covered filament end portion, said coil being arc shaped and lying in a plane transverse to the lamp axis.

5. A projection lamp comprising an incandescible coil filament of the bar type, curved slightly to the shape of an arc, in order to throw light of substantially constant intensity, from its convex side, with a variation along the length of the coil portion less than of that before bending, from angles from about 10 to one side to about 10 to the other side of a line normal to the filament at its midpoint.

6. A projection lamp comprising an envelope, at

from angles from about 10 mount secured therein, said mount having a press with leading-in conductors extending therethrough and terminating in supports, an incandescible coil filament of the bar type formed with substantially straight end portions extending in substantially opposite directions from the coil portion, and secured to the free end portions of said supports, the coil portion of said filament being curved slightly to the shape of an arc, in order to throw light of substantially constant intensity from its convex side, with a variation along the length of the coil portion less than 25% of that before bending, from angles from about 10 to one side to about 10 to the other side of aline normal to the filament at the midpoint.

the shape of an are lying in a plane transverse to the axis of the envelope, in order to avoid the relatively great variation in intensity along the length of a coil of the straight bar type, whereby said filament, when viewed from its convex'side, to one side to about 10 to the other side of a line normal to the filament at its midpointjhas a variation in intensity along its length of not more than four percent.

GJON .m 

